javascript - 迭代稀疏数组

Question

This answer表示迭代稀疏数组的最佳方法是使用 for X in Array

但是，当我尝试这个时，我绊倒了，因为 X 的类型是一个字符串，而不是我期望的整数索引。 (一切都很好，直到我将它添加到另一个整数......)

var arr = [];
arr[10000] = "Hello";

var shifted = []

for (var x in arr)
    shifted[10+x] = arr[x];

“预期”:

  shifted[10010] = "Hello

实际

  shifted["1010000"] = "Hello" 

是否有更好的方法使用索引迭代稀疏数组，或者我应该使用 Number(X)哪里需要？

Answer 1

这就是 V8(和其他 JavaScript 引擎)处理数组的方式:

V8 uses two different methods to handle arrays:

• Fast elements:
  Designed for arrays where set of keys are very compact. They have a linear storage buffer that can be accessed very efficiently.

• Dictionary elements:
  Designed for sparse arrays which don’t have every elements inside of them. It is actually a hash table, more expensive to access than “Fast Elements”

Source: http://thibaultlaurens.github.io/javascript/2013/04/29/how-the-v8-engine-works/

当您使用稀疏数组时，键将转换为字符串，然后进行哈希处理。如果您想要数字键:不要使用稀疏数组或手动将键转换为数字。